diff options
Diffstat (limited to 'gdb/i386-tdep.c')
| -rw-r--r-- | gdb/i386-tdep.c | 134 |
1 files changed, 134 insertions, 0 deletions
diff --git a/gdb/i386-tdep.c b/gdb/i386-tdep.c index 3e50ca8..2388790 100644 --- a/gdb/i386-tdep.c +++ b/gdb/i386-tdep.c @@ -722,6 +722,140 @@ i386v4_sigtramp_saved_pc (frame) } #endif /* I386V4_SIGTRAMP_SAVED_PC */ +#ifdef I386_LINUX_SIGTRAMP + +/* When the i386 Linux kernel calls a signal handler, the return + address points to a bit of code on the stack. This function + returns whether the PC appears to be within this bit of code. + + The instruction sequence is + pop %eax + mov $0x77,%eax + int $0x80 + or 0x58 0xb8 0x77 0x00 0x00 0x00 0xcd 0x80. + + Checking for the code sequence should be somewhat reliable, because + the effect is to call the system call sigreturn. This is unlikely + to occur anywhere other than a signal trampoline. + + It kind of sucks that we have to read memory from the process in + order to identify a signal trampoline, but there doesn't seem to be + any other way. The IN_SIGTRAMP macro in tm-linux.h arranges to + only call us if no function name could be identified, which should + be the case since the code is on the stack. */ + +#define LINUX_SIGTRAMP_INSN0 (0x58) /* pop %eax */ +#define LINUX_SIGTRAMP_OFFSET0 (0) +#define LINUX_SIGTRAMP_INSN1 (0xb8) /* mov $NNNN,%eax */ +#define LINUX_SIGTRAMP_OFFSET1 (1) +#define LINUX_SIGTRAMP_INSN2 (0xcd) /* int */ +#define LINUX_SIGTRAMP_OFFSET2 (6) + +static const unsigned char linux_sigtramp_code[] = +{ + LINUX_SIGTRAMP_INSN0, /* pop %eax */ + LINUX_SIGTRAMP_INSN1, 0x77, 0x00, 0x00, 0x00, /* mov $0x77,%eax */ + LINUX_SIGTRAMP_INSN2, 0x80 /* int $0x80 */ +}; + +#define LINUX_SIGTRAMP_LEN (sizeof linux_sigtramp_code) + +/* If PC is in a sigtramp routine, return the address of the start of + the routine. Otherwise, return 0. */ + +static CORE_ADDR +i386_linux_sigtramp_start (pc) + CORE_ADDR pc; +{ + unsigned char buf[LINUX_SIGTRAMP_LEN]; + + /* We only recognize a signal trampoline if PC is at the start of + one of the three instructions. We optimize for finding the PC at + the start, as will be the case when the trampoline is not the + first frame on the stack. We assume that in the case where the + PC is not at the start of the instruction sequence, there will be + a few trailing readable bytes on the stack. */ + + if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) + return 0; + + if (buf[0] != LINUX_SIGTRAMP_INSN0) + { + int adjust; + + switch (buf[0]) + { + case LINUX_SIGTRAMP_INSN1: + adjust = LINUX_SIGTRAMP_OFFSET1; + break; + case LINUX_SIGTRAMP_INSN2: + adjust = LINUX_SIGTRAMP_OFFSET2; + break; + default: + return 0; + } + + pc -= adjust; + + if (read_memory_nobpt (pc, (char *) buf, LINUX_SIGTRAMP_LEN) != 0) + return 0; + } + + if (memcmp (buf, linux_sigtramp_code, LINUX_SIGTRAMP_LEN) != 0) + return 0; + + return pc; +} + +/* Return whether PC is in a Linux sigtramp routine. */ + +int +i386_linux_sigtramp (pc) + CORE_ADDR pc; +{ + return i386_linux_sigtramp_start (pc) != 0; +} + +/* Assuming FRAME is for a Linux sigtramp routine, return the saved + program counter. The Linux kernel will set up a sigcontext + structure immediately before the sigtramp routine on the stack. */ + +CORE_ADDR +i386_linux_sigtramp_saved_pc (frame) + struct frame_info *frame; +{ + CORE_ADDR pc; + + pc = i386_linux_sigtramp_start (frame->pc); + if (pc == 0) + error ("i386_linux_sigtramp_saved_pc called when no sigtramp"); + return read_memory_integer ((pc + - LINUX_SIGCONTEXT_SIZE + + LINUX_SIGCONTEXT_PC_OFFSET), + 4); +} + +/* Assuming FRAME is for a Linux sigtramp routine, return the saved + stack pointer. The Linux kernel will set up a sigcontext structure + immediately before the sigtramp routine on the stack. */ + +CORE_ADDR +i386_linux_sigtramp_saved_sp (frame) + struct frame_info *frame; +{ + CORE_ADDR pc; + + pc = i386_linux_sigtramp_start (frame->pc); + if (pc == 0) + error ("i386_linux_sigtramp_saved_sp called when no sigtramp"); + return read_memory_integer ((pc + - LINUX_SIGCONTEXT_SIZE + + LINUX_SIGCONTEXT_SP_OFFSET), + 4); +} + +#endif /* I386_LINUX_SIGTRAMP */ + #ifdef STATIC_TRANSFORM_NAME /* SunPRO encodes the static variables. This is not related to C++ mangling, it is done for C too. */ |